1911 Encyclopædia Britannica/Pasteur, Louis

From Wikisource
Jump to navigation Jump to search

PASTEUR, LOUIS (1822–1895), French chemist, was born, on the 27th of December 1822, at Dôle, Franche-Comté, where his father carried on the business of a tanner. Shortly afterwards the Pasteur family removed to Arbois, where Louis attended the École primaire, and later the collège of that place. Here he apparently did not especially distinguish himself, belonging to the class of bons ordinaires. Fortunately at Arbois he came under the influence of an excellent teacher in the person of the director of the collège, who must have discerned in the quiet boy the germs of greatness, as he constantly spoke to him of his future career at the École normale in Paris. In October 1838 Louis was sent with a friend to the metropolis, to a school in the Quartier Latin, preparatory to the École normale. But he did not remain long in Paris, for being a nervous and excitable boy, his health broke down, and he yearned for his home in Franche-Comté. " If only I could smell the tannery once more," said he to his companions, " I should feel well." So home he went, though not for long, as his ambition was still to become a normalien, and to this end he entered the Royal College of Besançon, "en attendant l'heureux jour où je serais admis à l'école normale." Step by step he attained his end; in 1840 he won his "bachelier ès lettres," and shortly afterwards he received an appointment as assistant mathematical master in the college. Two years later he passed the examination for the "baccalauréat ès sciences" enabling him to become candidate for the École normale. But here something (probably the examiner) was at fault, for a note was attached to Pasteur's diploma stating that he was only " mediocre " in chemistry. In those early days and early trials the dominant note of Pasteur's life was sounded. To his sisters he writes: " Ces trois choses, la volonté, le travail, le succès, se partagent toute l'existence humaine. La volonté ouvre la porte aux carrier es brill antes et heureuses; le travail les franchit, et une fois arrivé au terme du voyage, le succes vient couronner l'œuvre." Throughout his life, and to the very end, " work " was his constant inspiration. On his deathbed he turned to the devoted pupils who watched over their master's last hours. " Où en êtes-vous?" he exclaimed. " Que faites-vous?" and ended by repeating his favourite words, " II faut travailler."

The first incentive to his serious study of chemistry was given by hearing J. B. A. Dumas lecture at the Sorbonne; and ere long he broke new ground for himself, A. J. Balard having given him an opportunity for chemical work by appointing him to the post of laboratory assistant. A few words of explanation concerning Pasteur's first research are necessary to give the key to all his future work. What was the secret power which enabled him to bring under the domain of scientific laws phenomena of disease which had so far bafHed human endeavour? It simply consisted in the application, to the elucidation of these complex problems, of the exact methods of chemical and physical research. Perhaps the most remarkable discovery of modern chemistry is the existence of compounds, which, whilst possessing an identical composition, are absolutely different bodies, judged of by their properties. The first of the numerous cases of isomerism now known was noted, but unexplained, by J. J. Berzelius. It was that of two tartaric acids, deposited from wine-lees. The different behaviour of these two acids to a ray of polarized light was subsequently observed by J. B. Biot. One possessed the power of turning the plane of the polarized ray to the right; the other possessed no rotary power. Still no explanation of this singular fact was forthcoming, and it was reserved for the young chemist from Franche-Comté to solve a problem which had baffled the greatest chemists and physicists of the time. Pasteur proved that the inactivity of the one acid depended upon the fact that it was composed of two isomeric constituents: one the ordinary or dextrorotary acid, and the other a new acid, which possessed an equally powerful left-handed action. The veteran Biot whose acquaintance Pasteur had made, was incredulous. He insisted on the repetition of the experiment in his presence; and when convinced of the truth of the explanation he exclaimed to the discoverer: " Mon cher enfant, j'ai tant aimé les sciences dans ma vie que cela me fait battre le cœur." Thus at one step Pasteur gained a place of honour among the chemists of the day, and was immediately appointed professor of chemistry at the Faculté of Science at Strasburg, where he soon afterwards married Mile Laurent, who proved herself to be a true and noble helpmeet. Next he sought to prepare the inactive form of the acid by artificial means; and after great and long-continued labour he succeeded, and was led to the commencement of his classical researches on fermentation, by the observation that when the inactive acid was placed in contact with a special form of mould (Penicillium glaucum) the right-handed acid alone was destroyed, the left-handed variety remained unchanged. So well was his position as a leading man of science now established that in 1854 he was appointed professor of chemistry and dean of the Faculte des Sciences at LiUe. In his inaugural address he used significant words, the truth of which was soon manifested in his case: " In the field of observation chance only favours those who are prepared." The diseases or sicknesses of beer and wine had from time immemorial baffled all attempts at cure. Pasteur one day visited a brewery containing both sound and unsound beer. He examined the yeasts under the microscope, and at once saw that the globules from the sound beer were nearly spherical, whilst those from the sour beer were elongated; and this led him to a discovery, the consequences of which have revolutionized chemical as well as biological science, inasmuch as it was the beginning of that wonderful series of experimental researches in which he proved conclusively that the notion of spontaneous generation is a chimera. Up to this time the phenomenon of fermentation was considered strange and obscure. Explanations had indeed been put forward by men as eminent as Berzelius and Liebig, but they lacked experimental foundation. This was given in the most complete degree by Pasteur. For he proved that the various changes occurring in the several processes of fermentation—as, for example, in the vinous, where alcohol is the chief product; in the acetous, where vinegar appears; and in the lactic, where milk turns sour—are invariably due to the presence and growth of minute organisms called ferments. Exclude every trace of these organisms, and no change occurs. Brewers' wort remains unchanged for years, milk keeps permanently sweet, and these and other complex liquids remain unaltered when freely exposed to air from which all these minute organisms are removed. " The chemical act of fermentation, " writes Pasteur, " is essentially a correlative phenomenon of a vital act beginning and ending with it."

But we may ask, as Pasteur did, Why does beer or milk become sour on exposure to ordinary air? Are these invisible germs which cause fermentation always present in the atmosphere? or are they not generated from the organic, but the non-organized constituents of the ferment able liquid? In other words, are these organisms not spontaneously generated? The controversy on this question was waged with spirit on both sides; but in the end Pasteur came off victorious, and in a series of the most delicate and most intricate experimental researches he proved that when the atmospheric germs are absolutely excluded no changes take place. In the interior of the grape, in the healthy blood, no such germs exist; crush the grape, wound the flesh, and expose them to the ordinary air, then changes, either fermentative or putrefactive, run their course. But place the crushed fruit or the wounded animal under conditions which preclude the presence or destroy the life of the germ, and again no change takes place; the grape juice remains sweet and the wound clean. The application of these facts to surgical operations, in the able hands of Lord Lister, was productive of the most beneficent results, and has indeed revolutionized surgical practice.

Pasteur was now the acknowledged head of the greatest chemical movement of the time, the recipient of honours both from his own country and abroad, and installed at the ficole normale in Paris in a dignified and important post. Not, however, was it without grave opposition from powerful friends in the .cademy that Pasteur carried on his work. Biot—who loved and admired him as a son—publicly announced that his enterprise was chimerical and the problem insoluble; Dumas evidently thought so too, for he advised Pasteur not to spend more of his time on such a subject. Yet he persevered: " Travailler, travailler toujours " was his motto, and his patience was rewarded by results which have not merely rendered his name immortal, but have benefited humanity in a way and to a degree for which no one could have ventured to hope. To begin with a comparatively small, though not unimportant, matter, Pasteur's discoveries on fermentation inaugurated a new era in the brewing and wine-making industries. Empiricism, hitherto the only guide, if indeed a guide at all, was replaced by exact scientific knowledge; the connexion of each phenomenon with a controllable cause was established, and rule-of-thumb and quackery banished for ever by the free gift to the world of the results of his researches.

But his powers of patient research and of quick and exact observation were about to be put to a severe test. An epidemic of a fatal character had ruined the French silk producers. Dumas, a native of the Alais district, where the disease was rampant, urged Pasteur to undertake its investigation. Up to that time he had never seen a silkworm, and hesitated to attempt so difficult a task; but at the reiterated request of his friend he consented, and in June 1865 went to the south of France for the purpose of studying the disease on the spot. In September of the same year he was able to announce results which pointed to the means of securing immunity from the dreaded plague. The history of this research, of the gradual elimination of the unimportant conditions, of the recognition of those which controlled the disease, is one of the most fascinating chapters of scientific discovery. Suffice it here to say that careful experiment and accurate observation succeeded in ascertaining the cause of the disease and in preventing its recurrence, thus bringing back to prosperity the silk trade of France, with all that this entails. " There is no greater charm," says Pasteur, " for the investigator than to make new discoveries; but his pleasure is heightened when he sees that they have a direct application to practical life." Pasteur had the good fortune, and just reward of seeing the results of his work applied to the benefit both of the human race and the animal world. It is to him that the world is indebted for the introduction of methods which have already worked wonders, and bid fair to render possible the preventive treatment of all infectious diseases. Just as each kind of fermentation possesses a definite organized ferment, so many diseases are dependent on the presence of a distinct microbe; and just as the gardener can pick out and grow a given plant or vegetable, so the bacteriologist can (in most cases) eliminate the adventitious and grow the special organism—in other words, can obtain a pure cultivation which has the power of bringing about the special disease. But by a process of successive and continued artificial cultures under different conditions, the virus of the organism is found to become attenuated; and when this weakened virus is administered, the animal is rendered immune against further attacks. The first disease investigated by Pasteur was that of chicken cholera, an epidemic which destroyed 10% of the French fowls; after the application of the preventative method the death-rate was reduced to below 1%. Next came the successful attempt to deal with the fatal cattle scourge known as anthrax. This is also caused by the presence of a microbe, of which the virus can also be attenuated, and by inoculation of this weakened virus the animal rendered immune. Many millions of sheep and oxen all over the world have thus been treated, and the rate of mortality reduced from 10 to less than 1%. As to the money value of these discoveries, T. H. Huxley gave it as his opinion that it was sufficient to cover the whole cost of the war indemnity paid by France to Germany in 1870.

The most interesting of Pasteur's investigations in preventive and curative medicine remains to be told. It is no less than a cure for the dread disease of hydrophobia in man of of rabies in animals; and the interest of the achievement is not only that he successfully combated one of the mysterious and most fell diseases to which man is subject, but also that this was accomplished in spite of the fact that this special microbe causing the disease had not been isolated. To begin with, Pasteur, in studying the malady in dogs, came to the conclusion that the injection of a portion of the matter of the spinal column of a rapid dog into the body of a healthy one produces in the latter with certainty the symptoms of rabies. The next step was to endeavour so as to modify and weaken the virus as to enable it to be used as a preventive or as an antitoxin. This, after and long serious labour, he effected; the dog thus inoculated proved to be immune when bitten by a rabid animal. But this was not enough. Would the inoculation of the attenuated virus have a remedial effect on an animal already bitten? If so, it might be possible to save the lives of persons bitten by mad dogs. Here again experiment was successful. A number of dogs were inoculated, the same number were untreated, and both sets were bitten by rabid animals. All the treated dogs lived; all the untreated dogs died from rabies. It was, however, one thing to experiment on dogs, and quite another to do so on human beings. Nevertheless Pasteur was bold enough to try. The trial was successful, and by doing so he earned the gratitude of the human race. Then, on the 14th of November 1888, the Institut Pasteur was founded. Thousands of people suffering from bites from rabid animals, from all lands, have been treated in this institute, and the death-rate from this most horrible of all diseases has been reduced to less than 1%. Not only in Paris, but in many other cities throughout the world, institutes on the model of the original one have been set up and are doing beneficent work, all arising from the genius and labour of one man. At the inauguration of the institute Pasteur closed his oration with the following words:—

" Two opposing laws seem to me now in contest. The one, a law of blood and death, opening out each day new modes of destruction, forces nations to be always ready for the battle. The other, a law of peace, work and health, whose only aim is to deliver man from the calamities which beset him. The one seeks violent conquests, the other the relief of mankind. The one places a single life above all victories, the other sacrifices hundreds of thousands of lives to the ambitions of a single individual. The law of which we are the instruments strives even through the carnage to cure the wounds due to the law of war. Treatment by our antiseptic methods may preserve the lives of thousands of soldiers. Which of these two laws will prevail, God only knows. But of this we may be sure, that science, in obeying the law of humanity, will always labour to engage the frontiers of life."

Rich in years and in honours, but simple-minded and affectionate as a child, this great benefactor to his species passed quietly away near St Cloud on the 28th of September 1895.

Mention need only be made of Pasteur's chief works, as follows: Études sur le vin (1866), Études sur le vinaigre (1868), Études sur le maladie des vers à soie (1870) Études sur le bière (1876). He began the practice of inoculation for hydrophobia in 1885.

Se Vie de Pasteur, by René Vallerey-Radot (Paris, 1900).

 (H. E. R.)